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.TH COMPRESS 1 "Feb 5, 2020"
.SH NAME
compress, uncompress, zcat \- compress, uncompress files or display expanded
files
.SH SYNOPSIS
.nf
\fBcompress\fR [\fB-fv/\fR] [\fB-b\fR \fIbits\fR] [\fIfile\fR]...
.fi

.LP
.nf
\fBcompress\fR \fB-c\fR [\fB-fv\fR] [\fB-b\fR \fIbits\fR] [\fIfile\fR]
.fi

.LP
.nf
\fBuncompress\fR [\fB-fv\fR] [\fB-c | -/\fR] [\fIfile\fR]...
.fi

.LP
.nf
\fBzcat\fR [\fIfile\fR]...
.fi

.SH DESCRIPTION
.SS "compress"
The \fBcompress\fR utility attempts to reduce the size of the named files by
using adaptive Lempel-Ziv coding. Except when the output is to the standard
output, each file is replaced by one with the extension \fB\&.Z\fR, while
keeping the same ownership modes, change times and modification times, ACLs,
and extended attributes. The compress utility also attempts to set the owner and
group of \fIfile\fR\fB\&.Z\fR to the owner and group of file, but does not fail
if this cannot be done. If appending the \fB\&.Z\fR to the file pathname would
make the pathname exceed \fB1023\fR bytes, the command fails. If no files are
specified, the standard input is compressed to the standard output.
.sp
.LP
The amount of compression obtained depends on the size of the input, the number
of \fIbits\fR per code, and the distribution of common substrings. Typically,
text such as source code or English is reduced by 50\(mi60%. Compression is
generally much better than that achieved by Huffman coding (as used in
\fBpack\fR(1)) and it takes less time to compute. The \fIbits\fR parameter
specified during compression is encoded within the compressed file, along with
a magic number to ensure that neither decompression of random data nor
recompression of compressed data is subsequently allowed.
.SS "uncompress"
The \fBuncompress\fR utility restores files to their original state after they
have been compressed using the \fBcompress\fR utility. If no files are
specified, the standard input is uncompressed to the standard output.
.sp
.LP
This utility supports the uncompressing of any files produced by
\fBcompress\fR. For files produced by \fBcompress\fR on other systems,
\fBuncompress\fR supports 9- to 16-bit compression (see \fB-b\fR).
.SS "zcat"
The \fBzcat\fR utility writes to standard output the uncompressed form of files
that have been compressed using \fBcompress\fR. It is the equivalent of
\fBuncompress\fR \fB-c\fR. Input files are not affected.
.SH OPTIONS
The following options are supported:
.sp
.ne 2
.na
\fB\fB-b\fR \fIbits\fR\fR
.ad
.RS 11n
Sets the upper limit (in bits) for common substring codes. \fIbits\fR must be
between 9 and 16 (16 is the default). Lowering the number of bits result in
larger, less compressed files.
.RE

.sp
.ne 2
.na
\fB\fB-c\fR\fR
.ad
.RS 11n
Writes to the standard output; no files are changed and no \fB\&.Z\fR files are
created. The behavior of \fBzcat\fR is identical to that of `\fBuncompress\fR
\fB-c\fR'.
.RE

.sp
.ne 2
.na
\fB\fB-f\fR\fR
.ad
.RS 11n
When compressing, forces compression of \fIfile\fR, even if it does not
actually reduce the size of the file, or if the corresponding
\fIfile\fR\fB\&.Z\fR file already exists.
.sp
If the \fB-f\fR option is not specified, and the process is not running in the
background, prompts to verify whether an existing file should be overwritten.
If the response is affirmative, the existing file is overwritten. When
uncompressing, does not prompt for overwriting files. If the \fB-f\fR option is
not specified, and the process is not running in the background, prompts to
verify whether an existing file should be overwritten. If the standard input is
not a terminal and \fB-f\fR is not specified, writes a diagnostic message to
standard error and exits with a status greater than \fB0\fR.
.RE

.sp
.ne 2
.na
\fB\fB-v\fR\fR
.ad
.RS 11n
Verbose. Writes to standard error messages concerning the percentage reduction
or expansion of each file.
.RE

.sp
.ne 2
.na
\fB\fB-/\fR\fR
.ad
.RS 11n
When compressing or decompressing, copies any extended system attributes
associated with the source file to the target file and copies any extended
system attributes associated with extended attributes of the source file to the
corresponding extended attributes associated with the target file. If any
extended system attributes cannot be copied, the original file is retained, a
diagnostic is written to \fBstderr\fR, and the final exit status is
\fBnon-zero\fR.
.RE

.SH OPERANDS
The following operand is supported:
.sp
.ne 2
.na
\fB\fIfile\fR\fR
.ad
.RS 8n
A path name of a file to be compressed by \fBcompress\fR, uncompressed by
\fBuncompress\fR, or whose uncompressed form is written to standard out by
\fBzcat\fR. If \fIfile\fR is \fB\(mi\fR, or if no \fIfile\fR is specified, the
standard input is used.
.RE

.SH USAGE
See \fBlargefile\fR(7) for the description of the behavior of \fBcompress\fR,
\fBuncompress\fR, and \fBzcat\fR when encountering files greater than or equal
to 2 Gbyte (2^31 bytes).
.SH ENVIRONMENT VARIABLES
See \fBenviron\fR(7) for descriptions of the following environment variables
that affect the execution of \fBcompress\fR, \fBuncompress\fR, and \fBzcat\fR:
\fBLANG\fR, \fBLC_ALL\fR, \fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR,
and \fBNLSPATH\fR.
.sp
.LP
Affirmative responses are processed using the extended regular expression
defined for the \fByesexpr\fR keyword in the \fBLC_MESSAGES\fR category of the
user's locale. The locale specified in the \fBLC_COLLATE\fR category defines
the behavior of ranges, equivalence classes, and multi-character collating
elements used in the expression defined for \fByesexpr\fR. The locale specified
in \fBLC_CTYPE\fR determines the locale for interpretation of sequences of
bytes of text data a characters, the behavior of character classes used in the
expression defined for the \fByesexpr\fR. See \fBlocale\fR(7).
.SH EXIT STATUS
The following error values are returned:
.sp
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 6n
Successful completion.
.RE

.sp
.ne 2
.na
\fB\fB1\fR\fR
.ad
.RS 6n
An error occurred.
.RE

.sp
.ne 2
.na
\fB\fB2\fR\fR
.ad
.RS 6n
One or more files were not compressed because they would have increased in size
(and the \fB-f\fR option was not specified).
.RE

.sp
.ne 2
.na
\fB\fB>2\fR\fR
.ad
.RS 6n
An error occurred.
.RE

.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
CSI	Enabled
_
Interface Stability	Committed
_
Standard	See \fBstandards\fR(7).
.TE

.SH SEE ALSO
.BR ln (1),
.BR pack (1),
.BR fgetattr (3C),
.BR fsetattr (3C),
.BR attributes (7),
.BR environ (7),
.BR largefile (7),
.BR locale (7),
.BR standards (7)
.SH DIAGNOSTICS
.ne 2
.na
\fBUsage: \fBcompress [-fv/] [-b\fR \fImaxbits\fR\fB]\fR [\fIfile\fR\|.\|.\|. ]\fR
.ad
.br
.na
\fB\fBcompress c [-fv] [-b\fR \fImaxbits\fR\fB]\fR [\fIfile\fR]\fR
.ad
.sp .6
.RS 4n
Invalid options were specified on the command line.
.RE

.sp
.ne 2
.na
\fBUsage: \fBuncompress [-fv] [-c | -/] [\fR\fIfile\fR\fB]...\fR\fR
.ad
.sp .6
.RS 4n
Invalid options were specified on the command line.
.RE

.sp
.ne 2
.na
\fBMissing maxbits\fR
.ad
.sp .6
.RS 4n
Maxbits must follow \fB-b\fR, or invalid maxbits, not a numeric value.
.RE

.sp
.ne 2
.na
\fB\fIfile\fR: not in compressed format\fR
.ad
.sp .6
.RS 4n
The file specified to \fBuncompress\fR has not been compressed.
.RE

.sp
.ne 2
.na
\fB\fIfile\fR: compressed with \fIxx\fRbits, can only handle \fIyy\fRbits\fR
.ad
.sp .6
.RS 4n
\fBfile\fR was compressed by a program that could deal with more \fIbits\fR
than the compress code on this machine. Recompress the file with smaller
\fIbits\fR.
.RE

.sp
.ne 2
.na
\fB\fIfile\fR: already has .\|Z suffix -- no change\fR
.ad
.sp .6
.RS 4n
The file is assumed to be already compressed. Rename the file and try again.
.RE

.sp
.ne 2
.na
\fB\fIfile\fR already exists; do you wish to overwrite (yes or no)?\fR
.ad
.sp .6
.RS 4n
Respond \fBy\fR if you want the output file to be replaced; \fBn\fR if not.
.RE

.sp
.ne 2
.na
\fBuncompress: corrupt input\fR
.ad
.sp .6
.RS 4n
A \fBSIGSEGV\fR violation was detected, which usually means that the input file
is corrupted.
.RE

.sp
.ne 2
.na
\fBCompression:\fIxx.xx\fR\fB%\fR\fR
.ad
.sp .6
.RS 4n
Percentage of the input saved by compression. (Relevant only for \fB-v\fR.)
.RE

.sp
.ne 2
.na
\fB- - not a regular file: unchanged\fR
.ad
.sp .6
.RS 4n
When the input file is not a regular file, (such as a directory), it is left
unaltered.
.RE

.sp
.ne 2
.na
\fB- - has \fIxx\fR other links: unchanged\fR
.ad
.sp .6
.RS 4n
The input file has links; it is left unchanged. See \fBln\fR(1) for more
information.
.RE

.sp
.ne 2
.na
\fB- - file unchanged\fR
.ad
.sp .6
.RS 4n
No savings are achieved by compression. The input remains uncompressed.
.RE

.sp
.ne 2
.na
\fB- -filename too long to tack on .Z\fR
.ad
.sp .6
.RS 4n
The path name is too long to append the \fB\&.Z\fR suffix.
.RE

.sp
.ne 2
.na
\fB- -cannot preserve extended attributes. file unchanged\fR
.ad
.sp .6
.RS 4n
Extended system attributes could not be copied.
.RE

.SH NOTES
Although compressed files are compatible between machines with large memory,
\fB-b\fR 12 should be used for file transfer to architectures with a small
process data space (64KB or less).
.sp
.LP
\fBcompress\fR should be more flexible about the existence of the \fB\&.\|Z\fR
suffix.
